Typical cable television system networks, such as for cable TV or CATV, include four main elements, a headend, a trunk system, a distribution system consisting of feeder cables bridged from the trunk system, and subscriber drops fed from broadband signal taps in the distribution system.
The headend, which is the central originating point of all signals carried on the network, receives signals from satellite, broadcasted, or transmitted by cable and transmits these signals as a broadband signal to numerous distribution nodes via trunk cables. Each distribution node, in turn, distributes the signals along with power, via feeder cables, with each feeder cable terminating at a termination block. Each feeder cable has numerous broadband signal taps inserted between the distribution node and the termination block. Each of these broadband signal taps draws a portion of the broadband signal and power for use by a subscriber, typically a home or business, and transmits the remaining broadband signal to the next tap along the feeder cable. Typically, there are hundreds, and sometimes thousands, of subscribers connected to each feeder cable. At a subscriber's site, the subscriber's equipment is connected to the tap via a drop cable, which may terminate directly into the television receiver on 12-channel systems, or into a converter where more than 12 channels are provided.
The individual broadband signal taps are connected in series along the feeder cable, the feeder cable being connected to an input terminal of the broadband signal tap. Within the broadband signal tap the broadband signal is split, and a small portion of the broadband signal is delivered to the subscriber through a subscriber drop cable. The remainder of the signal is returned to the feeder cable. By their very nature, these broadband signal taps are directional, so they must be installed so they can extract signal in the direction of the signal flow.
A disadvantage of prior broadband signal taps is that if one of the taps in a series of taps is out of service, the subscribers downstream of the out-of-service tap will be deprived of service. Service interruptions, even if for just a few milliseconds, can have serious and even catastrophic consequences for the transmission of digital data. Unlike analog signals, loss of even a small portion of a digital data transmission can render the transmission unintelligible, or cause a failure of the signals to reach the intended destination. With the advent of pay-per view and interactive television, and the increased use of cable systems for telephone voice and data transmission, it has become extremely important to provide means to maintain continuity of service to the subscribers.
Furthermore, the growth in the broadband industry has created a need for an infrastructure that can be readily modified and that can grow with the customer needs. Such modifications must be able to be provided with only minimal adverse impact to the existing customers. Thus, it is often necessary to add extra trunks, branches along the feeder cables or trunk lines, or to make other modifications to the system infrastructure. When this is done, it is often necessary to reverse the direction of signal flow along the feeder cables. This is typically accomplished by disconnecting the tap from the feeder cable and installing the tap in the opposite direction. Such a reversing of the tap, however, is a costly and time-consuming process that deprives hundreds or thousands of downstream subscribers of service during the time required to disconnect and reconnect the tap in the opposite direction.
Accordingly, there is a need for a broadband signal tap having a reversible directional coupler. Thus, if a change in the direction of the signal flow is required, such a reversal in signal direction is easily accomplished by merely changing the direction of the coupler, rather than removing the entire tap. Preferably, during the time required to reverse the directional coupler, there should not be any disturbance or interruption of service. Thus, there is a need for a broadband signal tap with a reversible directional coupler, which has a make-before-break connection such that the continuity of the broadband signal is maintained through the tap while the directional coupler is being reversed.